Surger blades are among the most replaced parts in the industrial sewing industry. The sewing speeds of today's overlock sewing equipment (also referred to as surgers) can reach up to 9500 stitches per minute. At these speeds both moving and stationary blades are susceptible to high tempertures, varying pressure between the blades, and chipping, leading to quick dulling of the blades. When these conditions occur, the fabric docs not cut cleanly. The blade must be continually sharpened. Often the blade must be sharpened every few days.
The use of high wear materials has greatly reduced the wear rates in surger blades. Carbide is the primary material used for those who seek better wearing blades. Presently the carbide is brazed onto the cutting end of the surger blade so as to reduce the amount of carbide material used. The expensive carbide material and the high cost of attaching the carbide to the steel fixture makes it difficult for many to afford to purchase these parts. Similarly, the use of ceramic as a cutting edge has the same drawbacks as carbide in that it is too expensive for many markets to purchase.
Horst Fenzi, U.S. Pat. No. 4,781,131, recognized the need for reducing the costs associated with surger blade wear. In his patent, he shows a multi-sided cutting blade which could be engaged in a blade holder in a plurality of positions corresponding to the multi-sided cutting edges. By loosening the mounting screw, he could rotate the blade to an unused cutting edge and therefore quickly eliminate downtime due to blade resharpening or blade replacement. Fenzi's teachings however, actually lead away from the teachings of the present invention because it specifically applies to an upper moving blade. The upper moving blade allows and in fact requires a thick mass at the area where Fenzi has his screw attaching means. This mass is required because as the leading edge of the moving upper blade moves past the cutting edge of the stationary blade, it must have enough mass to prevent breakage due to the high pressure of the opposing blade. Fenzi correctly designed the screw mounting means to be on the outside of the cutting edge, away from the opposing lower knife cutting edge. The lower stationary blade however, must remain thin to allow maximum adjustability relative to the needle and therefore allow for differing edge dimensions on the fabric being sewn. The mass that is required to utilize a screw mounting means is insufficient for a stationary lower blade and would cause cracking and breakage.